The present invention is directed to a serial thermal printer and, in particular, to a small-sized serial thermal printer having a thermal print head which is laterally movable and pressable against a platen having a sheet of thermal recording paper interposed therebetween for printing characters or smybols thereon.
Serial thermal printers print characters on a thermal recording paper or medium while pressing a thermal print head against the paper on a platen. When the sheet is to be advanced for printing on consecutive lines or otherwise, it is necessary to release the thermal head from pressing engagement with the sheet. One known construction for releasing the thermal head includes a feed screw or helical cam for driving the thermal head and a trigger electromagnet and clutch for releasing the platen and feeding the sheet of recording paper, such as is shown in Japanese Utility Model Laid-Open Publication No. 51-8139. According to another construction, the thermal print head is moved by a rope or string while the thermal head and platen are released by a plunger, such as is illustrated in Japanese Utility Model Laid-Open Publication No. 48-70525.
These conventional mechanisms are complex in structure and attempt to achieve a smaller size by arranging a drive motor horizontally inside or outside of the printer frame. A train of drive gears operatively coupled with the motor and an electromagnet and other parts are positioned outside of the frame in order to facilitate the attachment of the components in position. When the printer is to be installed in another device such as a desk top electronic calculator or the like, care must be exercised to place the printer with sufficient clearance provided therearound so that other parts will not contact the drive wheels and other members thereof. This constitutes an obstacle to efforts to make the overall device smaller in size. Accordingly, it is desired to provide an improved small-sized serial thermal printer which overcomes the problems associated with prior art constructions.